---
name: "uuencode"
section: "5"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd", "openbsd"]
url: "https://new.carta.tech/uuencode/5"
---

# uuencode(5)

format of an encoded uuencode file

## NAME

**uuencode** – format of an encoded uuencode file

## DESCRIPTION

Files output by [uuencode(1)](/uuencode/1.md) consist of a header line, followed by a number of body lines, and a trailer line. The [uudecode(1)](/uudecode/1.md) command will ignore any lines preceding the header or following the trailer. Lines preceding a header must not, of course, look like a header.

The header line is distinguished by having the first 6 characters “begin ” (note the trailing space). The word *begin* is followed by a mode (in octal), and a string which names the remote file. A space separates the three items in the header line.

The body consists of a number of lines, each at most 62 characters long (including the trailing newline). These consist of a character count, followed by encoded characters, followed by a newline. The character count is a single printing character, and represents an integer, the number of bytes the rest of the line represents. Such integers are always in the range from 1 to 45 or 64 and can be determined by subtracting the character space (octal 40) from the character. Character 64 represents a count of zero.

Groups of 3 bytes are stored in 4 characters, 6 bits per character. All characters are always in range from 1 to 64 and are offset by a space (octal 40) to make the characters printing. Character 64 represents a count of zero. The last line may be shorter than the normal 45 bytes. If the size is not a multiple of 3, this fact can be determined by the value of the count on the last line. Extra null characters will be included to make the character count a multiple of 4. The body is terminated by a line with a count of zero. This line consists of one ASCII backquote (octal 140) character.

The trailer line consists of “end” on a line by itself.

## SEE ALSO

[mail(1)](/mail/1.md), [uucp(1)](/uucp/1.md), [uudecode(1)](/uudecode/1.md), [uuencode(1)](/uuencode/1.md)

## HISTORY

The **uuencode** file format appeared in 4.0BSD.